Such an applicator is known from DE 10 2006 004 644 A1. The applicator applies a hardenable varnish on a surface of a substrate and in doing so also embosses it on its surface, whereby the varnish is provided with a microstructure. Such a varnish having a microstructure is also called riblet. The applicator has a circumferentially movable die having an embossing profile and is pressed by a robot against the surface, in particular the so-called substrate surface, and moved along the latter. The applicator has a roller inflatable by pressure on the outer circumference of which the die is firmly mounted and tensioned by the gas pressure. A hardening device directed towards the pressing area is arranged in the roller.